Brakes - need pumping

[Peter60]

I've been working on my 1968 G60 brakes for some time now and I'm unable to resolve why the brakes need pumping to work properly.

The setup is a single reservoir/circuit without power assist.

I have replaced the MC (I had it professionally re-sleeved and reconditioned), put in new slave cylinders front and rear, replaced the brake hoses and some brake lines yet when I push the brake pedal down it goes nearly to the floor. If I pump it the pressure increases and it doesn't go down as much and is acceptable. The brake shoes are fine, the brakes adjusted all round and I have bled the brake fluid numerous using manual bleeding and pressure bleeding. The pedal travel to engage the MC is minimal.

It shows all symptoms of having air in the line. When I bleed them again, no air comes out of the line.

When I clamp either the front or back brake hoses the brakes are fine. The pedal goes to an acceptable level. Initially I thought this narrowed down the problem to front or rear but since I get the same result for both the front and back it doesn't make sense.

The only thing I noticed is that when I push the pedal the first time the fluid in the reservoir drops slightly ( say 1/4 of an inch). This seems odd to me. When the pressure is off the fluid level returns.

I wonder if the MC really has the capacity to really work all the brakes or is it faulty?

I'm next going to convert it to a duel circuit MC (without power assist) and then finally with power assist. But before I do that I wondered if anyone could shed some insight into my problem.

[RiverPatrol]

For your '68 model G60 a single circuit master cylinder is standard. All of our US Patrol's are from the '60s and only have the single circuit master. Ours are also all SWBs with the small rear diff, but that shouldn't make a difference.

Even with the single circuit master, a properly bled and adjusted braking system will work very well. In my experience I have to bleed the system several times to get all of the air out. I follow the sequence of starting with the furthest wheel from the master and working my way to the closest.

Adjustment is also critical. I have seen people replace wheel cylinders when all that was needed is adjustment. The adjustment should be enough so the the wheel won't make a full revolution when spun by hand; it should turn only about half a revolution. You should hear the shoes dragging slightly.

Give it another look.

There is a thread that talks about upgrading to a dual master here, just search for it.

[Coyote Patrol]

It sounds like your brakes just need adjusted. Lift the vehicle with a jack and adjust the brakes until they just start to drag when you spin the wheel.

[Flaggoni]

It's unlikely, but could the master cylinder have been re-sleeved to a smaller size?
Perhaps 7/8" instead of 1"?
Also, master cyls often have a very light spring-loaded outlet check-valve meant to maintain a
very low residual pressure on the system's cup seals. (Not enough to move return springs)
If this check valve doesn't seal, slightly more pedal travel is required to take the initial 'slop' out of the
system. That check valve also aids during the manual bleeding of the system of air.
A clutch master cylinder doesn't have a check valve, which is why they are often difficult to bleed by pedal pumping.
( the fluid and air tend to just cycle back and forth in the lines instead of being pumped outward only)

[ckhorne]

I'm next going to convert it to a duel circuit MC (without power assist) and then finally with power assist. But before I do that I wondered if anyone could shed some insight into my problem.

You might want to read my thread here about upgrading to a dual MC with booster. I say this because even if you get everything perfect with your current brakes, you'll be undoing everything when you upgrade to either of those when you remove the lines. Everything will need to be re-bled. Also- boosting a dual circuit will be more complex (requiring two boosters) than boosting a dual MC.

It makes the most sense to go ahead and upgrade the way you plan at all once instead of in phases, unless you really like brake bleeding.

[Peter60]

Thanks all for the replies.

It sounds like adjusting the brakes might be worth another try, although I am sure I have done this many times.

Flaggoin. It is possible the MC has been resleaved a smaller dimension, but what you mention re check valve sounds more interesting. I will investigate both when I next work on the Patrol (its stored 500 miles from where I live - my next visit is scheduled mid January). I really would like to resolve the cause of my problem before I move onto a dual MC.

I have read the referenced articles in this forum. Thanks for the pointers and effort in getting these together.

Actually I don't mind bleeding the brakes. I use eezibleed.

eezibleed1.jpg

It works under pressure with air from a tire. It really is a one man bleeding system. I don't think this is the cause of my current problem as I have manually bleed the brakes many times as well. I find a bit higher pressure that what they recommend works best. I needed to build a clamp like bracket to hold the cap on the MC as the provided ones doesn't screw on correctly/tightly.

[Peter60]

I just spent half a day working on the brakes.

Since adjustment seemed the main suggestion I adjusted all brakes until they we locked on tight. Minimal movement in the brake pedal (as you would expect). I then adjusted all brakes off just one click. Wheels were able to move but there was a lot of drag. I slackened them all another click. Wheels then just had a small amount of drag. But the exciting thing was when I pressed the brake pedal it moved 1 to 2 inches. Pumping the brakes and there was no change. Brakes worked reasonable well. So I left it there. I think I can now get the vehicle registered - and drivable

In hindsight I did put one set of new brake linings on and the vehicle really hadn't been driven, so I guess the shoes haven't been run in yet. I also intend to get the brake drums honed to ensure they are the same sizes and round. I will then drive it a bit more and see if I need to adjust the brakes again.

Once I am confident with the brakes I will investigate a duel circuit MC and see how that works. If improvement is still needed the I will look at a power booster but that requires far more effort.

Thanks for all the suggestions below but it seemed the solution was adjustment.